BACKGROUND: The relationship between the pathogenic amyloid β-peptide species Aβ1-42 and tau pathology has been well studied and suggests that Aβ1-42 can accelerate tau pathology in vitro and in vivo. The manners if any in which Aβ1-40 interacts with tau remains poorly understood. In order to answer this question, we used cell-based system, transgenic fly and transgenic mice as models to study the interaction between Aβ1-42 and Aβ1-40.

RESULTS: In our established cellular model, live cell imaging (using confocal microscopy) combined with biochemical data showed that exposure to Aβ1-42 induced cleavage, phosphorylation and aggregation of wild-type/full length tau while exposure to Aβ1-40 didn't. Functional studies with Aβ1-40 were carried out in tau-GFP transgenic flies and showed that Aβ1-42, as previously reported, disrupted cytoskeletal structure while Aβ1-40 had no effect at same dose. To further explore how Aβ1-40 affects tau pathology in vivo, P301S mice (tau transgenic mice) were injected intracerebrally with either Aβ1-42 or Aβ1-40. We found that treatment with Aβ1-42 induced tau phosphorylation, cleavage and aggregation of tau in P301S mice. By contrast, Aβ1-40 injection didn't alter total tau, phospho-tau (recognized by PHF-1) or cleavage of tau, but interestingly, phosphorylation at Ser262 was shown to be significantly decreased after direct inject of Aβ1-40 into the entorhinal cortex of P301S mice.

CONCLUSIONS: These results demonstrate that Aβ1-40 plays different role in tau pathogenesis compared to Aβ1-42. Aβ1-40 may have a protective role in tau pathogenesis by reducing phosphorylation at Ser262, which has been shown to be neurotoxic.